Sweetening gasoline



Patented Mar. 25, 1941 PATENT OFFICE 2,236,080 SWEETENING GASOLINE Charles Wirth, III, and William B. Shanley, Chicago, Ill., assignors to Universal Oil Products Company, Chicago, 111., a corporation of Dela were No Drawing.

1 Claim.

This invention concerns a process for sweetening hydrocarbon distillates and more particularly, zthoseof gasoline boiling range.

More specifically, the process relates to the sweetening of both straight-run and cracked gasolines by means of the same body of coppercontaining sweetening reagent.

Among the processes which have been developed for improving the odor and doctor test of motor fuels is the so-called copper sweetening process wherein mercaptans contained in the gasoline are converted to the corresponding disulfides. Both solutionsand solid granular or powdered sweetening reagents have been used for this purpose. The present invention more particularly concerns processes the solid reagents.

When utilizing this type of process, the gasoline to be sweetened is usually mixed with oxygen or oxygen-containing gas such as air and passed through a bed of granular sweetening re: agent, or under otherconditions, contactedwith a slurry of powdered sweetening reagent. This mode of operation permits a more or less continuous operation of the plant, since the sweetening reagent is continuously regenerated. However, regeneration is not entirely complete during such operation and it is usually necessary at intervals to supplement the treatment with a period during which the gasoline flow is stopped and the sweetening reagent is blown with air or oxygen to increase its activity.

During the sweetening of gasolines and particularly cracked gasolines which are otherwise untreated, there is often a gradual accumulation of highly colored material on the copper sweetening reagent. Ordinarily, this material is not soluble in the gasoline until after it has been blown with air for a considerable length of time which as stated above, is necessary, whereupon a portion of it becomes readily soluble and dissolves in the gasoline when the sweetening operation is resumed. As a result, the gasoline is not only discolored, but also undergoes a considerable depreciation in its desirable properties, such as storage stability. As a consequence, it has been the practice in commercial operation to wash the sweetening reagent following the air blowing step with gasoline, which is then discarded or returned to the fractionating column, in order to remove these undesirable colored compounds. A considerable waste of gasoline results, as well as inconvenience in the operation and increased treating costs.

In one specific embodiment the present inveninvolving the use of Application September 8, 1939, Serial No. 293,926

tion comprises a process for sweetening gasoline which comprises mixing said gasoline with oxygen or an oxygen containing gas, contacting the mixture with a solid copper containing sweetening reagent in a primary treating step, separating residual oxygen therefrom, contacting the gasoline with a reagent to remove dissolved copper in a secondary treating step, the primary treating step of said process being subjected to the following repeated sequence of operations; (a) sweetening of cracked gasoline, (1)) sweetening of straight-run gasoline, and (c) regeneratingthe reagent with air in the absence of added gasoline.

The copper sweetening reagent may comprise any suitable solid, powdered, or granular reagent. Examples of these are mixtures of copper sulfate and ammonium chloride, inert fillers or carriers impregnated with suitable copper salts such as cupric chloride or other suitable halides of copper, and the like. When employing granular reagents, it isthe practice to place the reagent in a tower as a packing material and-percolate the gasoline to be sweetened through the reagent. Air or oxygen is added together with the gasoline and sufficient pressure is maintained to keep the 'gas substantially in solution in the gasoline. Normally this is of the order of 30-100 pounds per square inch. Normally 2-10 cubic feet of air or its equivalent of oxygen areadded per barrel of gasoline chargedl.

When using powdered reagents, a slurry is made of the reagent with ithe gasoline in the presence of air and after the sweetening operation is complete the reagent is separated by suitable means, such as filter presses, etc. The reagent may be recirculated as a slurry or may be maintained as a layer on a filter plate through which the gasoline is passed.

The sweetening reaction is normally carried out at :a temperature of approximately -120" F. and preferably at -90 F.

After the copper sweetening step, the residual air is separated from the gasoline and if copper is present, this is removed by treatment with a suitable secondary treating reagent such as a heavy metal sulfide, including zinc or iron sulfides, or an alkalior alkaline-earth metal sulfide.

The usual cycle of operation is carried out during the period of one operating day. Cracked gasoline is mixed with air and passed over the copper sweetening reagent which may consist, for example, of a granular reagent disposed in a tower. This is followed by separation of the residual air, and a secondary treatment is given the cracked gasoline to remove dissolved copper. This operation is carried out over a period of approximately 8-10 hours, the size of the plant, particularly in small refineries, usually being such as to permit sweetening of the entire refinery production of cracked gasolineduring this interval of time. sweetening of the cracked gasoline is then followed by treatment of straightrun gasoline over a period of time of similar magnitude, during which the plant production of straight-run gasoline for one day is sweetened. At the end of this time, the gasoline flow is discontinued and the reagent is blown with air to regenerate it for a period of 4-8 hours The cycle is repeated starting with the cracked gasoline. Occasionally it is necessary to discard the first few gallons of gasoline charged but the quantity is much reduced over that usually used for washing, and many times no gasoline is discarded.

This process has been found to have the advantage of substantially preventing discoloration and depreciation of the gasoline and sweetening reagent, with the result that the products are of improved quality and the life of the reagent is materially lengthened. The gasoline needed fol washing the reagent subsequent to the regeneration step is minimized. Furthermore, the process has the advantage in small refineries that a single sweetening plant can be used to treat both the straight-run and cracked gasoline produced. This results in a material saving in installation costs.

The following example is given to illustrate the usefulness and practicability of our process, but should not be construed as limiting it to the exact conditions or reagents used therein.

Untreated cracked gasoline from a Kansas crude oil was sweetened by contacting with a reagent consisting of a mixture of copper sulfate, ammonium chloride and pumice. The gasoline was mixed with 6 cu. ft. of air per barrel of gasoline and passed over the reagent at a pressure of pounds per square inch. After passage through the tower, the residual air was separated and the gasoline passed through a secondary treating agent consisting of zinc sulfide deposited on pumice in order to remove small quantities of dissolved copper. This operation was continued for a period of 10 hours, The flow of cracked gasoline was discontinued and sour straight-run gasoline which had been accumulating in storage tanks over this period of time, was sweetened. The sweetening of straight-run gasoline continued for 8 hours, during which one days production of gasoline was sweetened. The sweetening tower was then drained of gasoline and blown with air for a period of 6 hours, after which the cycle was resumed by sweetening of cracked gasoline which had been accumulating during this interval.

The entire production of straight-run and cracked gasoline when operating in this manner was of marketable quality, and it was unnecessary to discard gasoline at any time during the reaction.

Prior to installing this type of operation, the cracked gasoline had been sweetened with the identical reagent in a similar plant, the operation consisting of sweetening for approximately 18 hours, followed by air blowing for 6 hours. It was necessary to wash the reagent with straightrun gasoline, which was highly discolored and was discarded. As a consequence, the total treating cost was increased considerably. Furthermore, with this type of operation it was necessary to have a separate treating plant for sweetening the straight-run gasoline. Under these latter conditions the total life of the sweetening reagent was approximately 23,000 barrels per ton of reagent.

When operating according to the process of the present invention, a yield of 47,000 barrels per ton of reagent was obtained.

We claim as our invention:

In the sweetening of sour gasoline distillates by treatment with solid copper-containing sweet- 3 emng agents, the improved cycle of operation CHARLES VIIRTH, III. WILLIAM B. SHANLEY. 

